Datasheet

MAX1192
Ultra-Low-Power, 22Msps, Dual 8-Bit ADC
______________________________________________________________________________________ 21
Using Transformer Coupling
An RF transformer (Figure 8) provides an excellent
solution to convert a single-ended source signal to a
fully differential signal, required by the MAX1192 for
optimum performance. Connecting the center tap of the
transformer to COM provides a V
DD
/2 DC level shift to
the input. Although a 1:1 transformer is shown, a step-
up transformer can be selected to reduce the drive
requirements. A reduced signal swing from the input
driver, such as an op amp, can also improve the overall
distortion.
In general, the MAX1192 provides better SFDR and
THD with fully differential input signals than single-
ended drive, especially for high input frequencies. In
differential input mode, even-order harmonics are lower
as both inputs (INA+, INA- and/or INB+, INB-) are bal-
anced, and each of the ADC inputs only requires half
the signal swing compared to single-ended mode.
Single-Ended AC-Coupled Input Signal
Figure 9 shows an AC-coupled, single-ended applica-
tion. Amplifiers such as the MAX4108 provide high
speed, high bandwidth, low noise, and low distortion to
maintain the input signal integrity.
Buffered External Reference Drives
Multiple ADCs
The buffered external reference mode allows for more
control over the MAX1192 reference voltage and allows
multiple converters to use a common reference. To
drive one MAX1192 in buffered external reference
mode, the external circuit must sink 0.7µA, allowing one
reference circuit to easily drive the REFIN of multiple
converters to 1.024V ±10%.
MAX1192
T1
N.C.
V
IN
6
1
5
2
43
22pF
22pF
0.1μF
0.1μF
2.2μF
25Ω
25Ω
MINICIRCUITS
TT1-6-KK81
T1
N.C.
V
IN
6
1
5
2
4
3
22pF
22pF
0.1μF
0.1μF
2.2μF
25Ω
25Ω
MINICIRCUITS
TT1-6-KK81
INA-
INA+
INB-
INB+
COM
Figure 8. Transformer-Coupled Input Drive
MAX1192
0.1μF
1kΩ
1kΩ
100Ω
100Ω
C
IN
22pF
C
IN
22pF
INB+
INB-
COM
INA+
INA-
0.1μF
R
ISO
50Ω
R
ISO
50Ω
REFP
REFN
V
IN
MAX4108
0.1μF
1kΩ
1kΩ
100Ω
100Ω
C
IN
22pF
C
IN
22pF
0.1μF
R
ISO
50Ω
R
ISO
50Ω
REFP
REFN
V
IN
MAX4108
Figure 9. Using an Op Amp for Single-Ended, AC-Coupled
Input Drive